1. Field of the Invention
The present invention generally relates to a lens and an optical apparatus, and more particularly, to a fixed-focus lens and an apparatus integrating optical projection and image detection.
2. Description of Related Art
With the progress in science and technology, all kinds of optical products, such as digital cameras, digital camcorders, facsimile machines, photostat machines, optical disc players, scanners, rear projection display devices, and so on, have been gradually available to all in the daily lives while performance of the products is continually enhanced, and costs of the products are tinually reduced. Moreover, as the optical technology is highly developed, the rear projection display device is further developed to have integrated functions of optical projection and image detection. Image frames are generated by projecting a visible light on a screen, and positions and movements of fingers touching the screen are detected by means of an infrared detector, so that the function of a touch screen is achieved.
Since image frames displayed on a digital micro-mirror device (DMD) or a liquid-crystal-on-silicon panel (LCOS panel) are enlarged by a fixed-focus lens in the rear projection display device, the enlarged image frames are able to be displayed on the product with lower cost. However, in a conventional touch rear projection display device, since view angle of the fixed-focus lens is restricted, an image beam from the DMD or the LCOS panel is enlarged to an enough size after traveling a necessary distance, so that the enlarged image frame is displayed on the screen. On the other hand, infrared rays (IR) reflected by the screen also have to travel a necessary distance, so that IR images on a large-size screen are generated on a small-sized charge coupled device (CCD) or a small-sized complementary metal-oxide-semiconductor sensor (CMOS sensor). The necessary distance usually results in an excessive thickness of the rear projection display device, such that the rear projection display device may hardly compete with current flat panel displays.